The serine protease inhibitor PAI-1 is one of the primary inhibitors of the fibrinolytic system. The fibrinolytic system includes the proenzyme plasminogen, which is converted to the active enzyme, plasmin, by one of two tissue type plasminogen activators, t-PA or u-PA. PAI-1 is the principal physiological inhibitor of t-PA and u-PA. One of plasmin's main responsibilities in the fibrinolytic system is to digest fibrin at the site of vascular injury. The fibrinolytic system, however, is not only responsible for the removal of fibrin from circulation but is also involved in several other biological processes including ovulation, embryogenesis, intima proliferation, angiogenesis, tumorigenesis, and atherosclerosis.
Elevated levels of PAI-1 have been associated with a variety of diseases and conditions including those associated with impairment of the fibrinolytic system. For example, elevated levels of PAI-1 have been implicated in thrombotic diseases, e.g., diseases characterized by formation of a thrombus that obstructs vascular blood flow locally or detaches and embolizes to occlude blood flow downstream. (Krishnamurti, Blood, 69, 798 (1987); Reilly, Arteriosclerosis and Thrombosis, 11, 1276 (1991); Carmeliet, Journal of Clinical Investigation, 92, 2756 (1993), Rocha, Fibrinolysis, 8, 294, 1994; Aznar, Haemostasis 24, 243 (1994)). Antibody neutralization of PAI-1 activity resulted in promotion of endogenous thrombolysis and reperfusion (Biemond, Circulation, 91, 1175 (1995); Levi, Circulation 85, 305, (1992)). Elevated levels of PAI-1 have also been implicated in diseases such as polycystic ovary syndrome (Nordt, Journal of clinical Endocrinology and Metabolism, 85, 4, 1563 (2000)), bone loss induced by estrogen deficiency (Daci, Journal of Bone and Mineral Research, 15, 8, 1510 (2000)), cystic fibrosis, diabetes, chronic periodontitis, lymphomas, diseases associated with extracellular matrix accumulation, malignancies and diseases associated with neoangiogenesis, inflammatory diseases, vascular damage associated with infections, and diseases associated with increased uPA levels such as breast and ovarian cancer.
In view of the foregoing, there exists a need for the identification of inhibitors of PAI-1 activity and for methods of using the identified inhibitors to modulate PAI-1 expression or activity in a subject in order to treat disorders associated with elevated PAI-1 levels.